C/2011 J3 (LINEAR) was discovered on 2011, May 14.38 by the LINEAR survey with a 1.0-m f/2.15 reflector + CCD.
It was subsequently placed on the NEO Confirmation Page of the Minor Planet Center under the temporary designation BZ39121.
I was able to image it only 5 days after the discovery, on the night between May 19 and 20; fortunately it was still in the NEO Confirmation Page, located in the sky on the border between Cygnus and Cepheus.
The sky was clear with good seeing but the Moon interefered with the observations, as you can see from the gradient on the image below (92% Moon about 90° away), but nontheless I could quite easily confirm its cometary feature.
In this stack (16 min of total exposure time) the comet has a FWHM 50% larger than stars nearby of similar brightness, with a 10″ round and diffuse coma, with no visible tail.
The discovery was announced on IAUC 9209 (subscription required) and the astrometry published on MPEC 2011-K11.
Below is the image: